研究發現 生過孩子的女性在生理上會更老

Women who give birth may be biologically "older" than women who don't, a new study suggests.

一項新研究表明，生過孩子的女性在生理上會比那些沒有生過的“更老”。

For the study, the researchers analyzed information from 1,556 US women ages 20 to 44 who took part in a national survey from 1999 to 2002, which involved giving blood samples.

在該研究中，研究人員們分析了1556名20-44歲之間的美國女性的信息，她們參加了1999年至2002年期間的全國調查，並給出了血液樣本。

The researchers looked at the genetic material inside the women's cells, specifically the length of their telomeres. These are caps on the ends of chromosomes that protect the chromosomes from damage.

研究人員們觀察了這些女性細胞內的遺傳物質，尤其是她們端粒的長度。這些位於染色體末端的小帽子能夠保護染色體不受損。

Telomeres naturally shorten as people age, but the structures don't shorten at the same rate in every person. The longer a person's telomeres are, the more times their cells could hypothetically still divide, research has shown.

人們在變老的過程中，端粒也會自然縮短，但這個結構在每個人身上變短的速度均不同。研究表明，一個人的端粒越長，他們的細胞理論上能夠分裂的次數就越多。

Thus, telomeres are considered a marker of biological age — that is, the age of a person's cells, rather than the individual's chronological age.

因此，端粒也被科學家們視爲生理年齡的標記，即一個人的細胞年齡，而不是他們的實際年齡。

Women in the survey who said they'd given birth to at least one child had telomeres that were about 4 percent shorter, on average, than those of women who'd never given birth.

在研究中，至少生過一個孩子的女性端粒長度平均比那些未生產過的女性短百分之四。

The findings held even after the researchers took into account other factors that could affect telomere length, including the women's chronological age, body mass index and smoking habits.

即便研究人員們考慮了其它能影響端粒長度的因素（比如她們的實際年齡、身體質量指數和吸菸習慣），這些發現依舊站得住腳。

These findings suggest that a "history of live birth may be associated with shorter telomeres," the researchers wrote in their abstract, which was presented at the meeting of the American Public Health Association in Denver.

這些發現表明生產史可能與更短的端粒之間存在着聯繫。該研究的概述是在美國公共衛生協會於丹佛市舉辦的會議上發佈的。

The study was not designed to determine the reason behind the link, the researchers said. But one hypothesis is that having children increases stress levels, and high stress has been linked with shorter telomeres, the scientists said.

該研究並未探究這一聯繫背後的原因，但有猜測認爲生孩子會增加女性的壓力，而高壓與更短的端粒有關。

It is possible that pregnancy, birth and child-rearing can induce chronic stress, leading to shorter telomere length perhaps through an inflammatory pathway, said study researcher Anna Pollack, an assistant professor and environmental and reproductive epidemiologist at George Mason University.

美國喬治梅森大學的助教、生態環境與生殖流行病學家安娜·波萊克參與了該研究，她表示：“有可能懷孕、生產和撫養孩子帶來了慢性壓力，並通過炎症通路縮短了端粒長度。”

However, because the survey was conducted at a single point in time, the researchers cannot determine which came first in the women's lives — giving birth or having shorter telomeres. It's also possible that for some yet-unknown reason, women with shorter telomeres are more likely than women with longer ones to have children, Pollack said.

波萊克稱，但是由於調查是在某個時間點開展的，研究人員們無法確定生孩子與更短的端粒長度之間，哪一個先出現。有可能出於某些未知的原因，端粒更短的女性比端粒更長的女性更有可能生孩子。

More studies are needed that follow women over time and measure the length of their telomeres before, during and after pregnancy, she said.

她表示，還需要進一步的追蹤研究來確定女性的端粒在生孩子之前、懷孕期間和產後的長度。